Synchronized Audio Mixing

ABSTRACT

A first example playback device includes one or more processors and a non-transitory computer-readable medium storing instructions that, when executed by the one or more processors, cause the first playback device to perform functions. The functions include generating a mixed audio signal comprising one or more components of a first audio stream and one or more components of a second audio stream; and playing the mixed audio signal, where the one or more components of the second audio stream of the mixed audio signal played by the first playback device are played in synchrony with a second playback device configured to play the second audio stream. An example non-transitory computer-readable medium and an example method, both related to the first example playback device, are also disclosed herein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 120 to, is acontinuation of U.S. patent application Ser. No. 16/545,005, filed onAug. 20, 2019, and entitled “Synchronized Audio Mixing,” which isincorporated herein by reference in its entirety.

U.S. patent application Ser. No. 16/545,005 claims priority under 35U.S.C. § 120, and is a continuation of U.S. patent application Ser. No.15/935,966, filed on Mar. 26, 2018, entitled “Synchronized AudioMixing,” and issued as U.S. Pat. No. 10,387,110 on Aug. 20, 2019, whichis incorporated herein by reference in its entirety.

U.S. patent application Ser. No. 15/935,966 claims priority under 35U.S.C. § 120, and is a continuation of U.S. patent application Ser. No.15/607,507, filed on May 28, 2017, entitled “Synchronized Audio Mixing,”and issued as U.S. Pat. No. 9,977,649 on May 22, 2018; which isincorporated herein by reference in its entirety.

U.S. Pat. No. 15/607,507 claims priority under 35 U.S.C. § 120, and is acontinuation of U.S. patent application Ser. No. 14/617,604, filed onFeb. 9, 2015, entitled “Synchronized Audio Mixing,” and issued as U.S.Pat. No. 9,665,341 on May 30, 2017, which is incorporated herein byreference in its entirety.

FIELD OF THE DISCLOSURE

The disclosure is related to consumer goods and, more particularly, tomethods, systems, products, features, services, and other elementsdirected to media playback or some aspect thereof.

BACKGROUND

Options for accessing and listening to digital audio in an out-loudsetting were limited until in 2003, when SONOS, Inc. filed for one ofits first patent applications, entitled “Method for Synchronizing AudioPlayback between Multiple Networked Devices,” and began offering a mediaplayback system for sale in 2005. The Sonos Wireless HiFi System enablespeople to experience music from many sources via one or more networkedplayback devices. Through a software control application installed on asmartphone, tablet, or computer, one can play what he or she wants inany room that has a networked playback device. Additionally, using thecontroller, for example, different songs can be streamed to each roomwith a playback device, rooms can be grouped together for synchronousplayback, or the same song can be heard in all rooms synchronously.

Given the ever growing interest in digital media, there continues to bea need to develop consumer-accessible technologies to further enhancethe listening experience.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, aspects, and advantages of the presently disclosed technologymay be better understood with regard to the following description,appended claims, and accompanying drawings where:

FIG. 1 shows an example media playback system configuration in whichcertain embodiments may be practiced;

FIG. 2 shows a functional block diagram of an example playback device;

FIG. 3 shows a functional block diagram of an example control device;

FIG. 4 shows an example controller interface;

FIG. 5 shows a flow diagram for an example method;

FIG. 6 shows example functions of playback devices;

FIG. 7 shows example audio stream data and computation results forgenerating a mixed audio signal; and

FIG. 8 shows an example fade-in gain curve and an example fade-out gaincurve.

The drawings are for the purpose of illustrating example embodiments,but it is understood that the inventions are not limited to thearrangements and instrumentality shown in the drawings.

DETAILED DESCRIPTION I. Overview

In various situations, a first playback device may play a mixed audiostream that includes a first audio stream and a second audio stream. Itmay be useful for the first playback device to play the mixed audiostream in synchrony with a second playback device that plays a mixed orunmixed audio stream that includes at least the second audio stream. Inexamples where both the first and second playback devices play arespective mixed audio stream, it may be advantageous for the first andsecond playback devices to generate their own respective mixed audiostreams instead of receiving mixed audio streams from a third device.

For example, the first playback device may play a first mixed audiostream “AB” that includes an audio stream “A” and an audio stream “B.”The first playback device may play the first mixed audio stream “AB” insynchrony with the second playback device playing a second mixed audiostream “BC” that includes the audio stream “B” and an audio stream “C.”In some examples, this may involve a third device (e.g., a mixer oranother playback device) (i) generating the first mixed audio stream“AB” and providing the first mixed audio stream “AB” to the firstplayback device, and (ii) generating the second mixed audio stream “BC”and providing the second mixed audio stream “BC” to the second playbackdevice. The third device may also provide timing information to thefirst and second playback devices to facilitate synchronous (withrespect to the audio stream “B”) playback of the audio streams “AB” and“BC.”

For example, initially the first playback device may be playing theaudio stream “A,” (e.g., classical music) and the second playback devicemay be playing the audio stream “C” (e.g., jazz music). Then, the firstplayback device may begin playing the first mixed audio stream “AB” andthe second playback device may begin playing back the second mixed audiostream “BC.” In this example, audio stream “B” may be an alarm ringtone.The result of this process may be that the first playback device playsthe first mixed audio stream that includes classical music and the alarmringtone, while the second playback device plays the second mixed audiostream that includes jazz music and the alarm ringtone. Notwithstandingthat the first playback device may play the classical music withoutregard to playback of the jazz music by the second playback device, thefirst and second playback devices may play the alarm ringtone insynchrony.

However, it is possible that generating both the first mixed audiostream “AB” and the second mixed audio stream “BC” may consume asubstantial amount (or all) of the processing capacity of the thirddevice. Therefore, it may be desirable to have the first and secondplayback devices generate their own respective mixed audio streams usingtheir own respective processor(s). The first and second playback devicesgenerating their own respective mixed audio streams may enableprocessing capacity of the third device to be used for otherapplications.

Accordingly, some examples described herein involve, among other things,a first playback device (i) playing a first audio stream while also (ii)playing a second audio stream in synchrony with a second playbackdevice. The first and second playback devices may both access commontiming information that facilitates synchronous playback of the secondaudio stream by the first and second playback devices. Other aspects ofthe examples will be made apparent in the remainder of the descriptionherein.

In one aspect, a first example playback device includes one or moreprocessors and a non-transitory computer-readable medium storinginstructions that, when executed by the one or more processors, causethe first playback device to perform functions. The functions includegenerating a mixed audio signal comprising one or more components of afirst audio stream and one or more components of a second audio stream;and playing the mixed audio signal, where the one or more components ofthe second audio stream of the mixed audio signal played by the firstplayback device are played in synchrony with a second playback deviceconfigured to play the second audio stream.

In yet another aspect, an example non-transitory computer-readablemedium stores instructions that, when executed by a first playbackdevice, cause the first playback device to perform functions. Thefunctions include generating a mixed audio signal comprising one or morecomponents of a first audio stream and one or more components of asecond audio stream; and playing the mixed audio signal, where the oneor more components of the second audio stream of the mixed audio signalplayed by the first playback device are played in synchrony with asecond playback device configured to play the second audio stream.

In yet another aspect, an example method includes generating, by a firstplayback device, a mixed audio signal comprising one or more componentsof a first audio stream and one or more components of a second audiostream; and playing, by the first playback device, the mixed audiosignal, where the one or more components of the second audio stream ofthe mixed audio signal played by the first playback device are played insynchrony with a second playback device configured to play the secondaudio stream.

It will be understood by one of ordinary skill in the art that thisdisclosure includes numerous other embodiments. While some examplesdescribed herein may refer to functions performed by given actors suchas “users” and/or other entities, it should be understood that this isfor purposes of explanation only. The claims should not be interpretedto require action by any such example actor unless explicitly requiredby the language of the claims themselves.

II. Example Operating Environment

FIG. 1 shows an example configuration of a media playback system 100 inwhich one or more embodiments disclosed herein may be practiced orimplemented. The media playback system 100 as shown is associated withan example home environment having several rooms and spaces, such as forexample, a master bedroom, an office, a dining room, and a living room.As shown in the example of FIG. 1 , the media playback system 100includes playback devices 102, 104, 106, 108, 110, 112, 114, 116, 118,120, 122, and 124, control devices 126 and 128, and a wired or wirelessnetwork router 130.

Further discussions relating to the different components of the examplemedia playback system 100 and how the different components may interactto provide a user with a media experience may be found in the followingsections. While discussions herein may generally refer to the examplemedia playback system 100, technologies described herein are not limitedto applications within, among other things, the home environment asshown in FIG. 1 . For instance, the technologies described herein may beuseful in environments where multi-zone audio may be desired, such as,for example, a commercial setting like a restaurant, mall or airport, avehicle like a sports utility vehicle (SUV), bus or car, a ship or boat,an airplane, and so on.

a. Example Playback Devices

FIG. 2 shows a functional block diagram of an example playback device200 that may be configured to be one or more of the playback devices102-124 of the media playback system 100 of FIG. 1 . The playback device200 may include a processor 202, software components 204, memory 206,audio processing components 208, audio amplifier(s) 210, speaker(s) 212,and a network interface 214 including wireless interface(s) 216 andwired interface(s) 218. In one case, the playback device 200 might notinclude the speaker(s) 212, but rather a speaker interface forconnecting the playback device 200 to external speakers. In anothercase, the playback device 200 may include neither the speaker(s) 212 northe audio amplifier(s) 210, but rather an audio interface for connectingthe playback device 200 to an external audio amplifier or audio-visualreceiver.

In one example, the processor 202 may be a clock-driven computingcomponent configured to process input data according to instructionsstored in the memory 206. The memory 206 may be a tangiblecomputer-readable medium configured to store instructions executable bythe processor 202. For instance, the memory 206 may be data storage thatcan be loaded with one or more of the software components 204 executableby the processor 202 to achieve certain functions. In one example, thefunctions may involve the playback device 200 retrieving audio data froman audio source or another playback device. In another example, thefunctions may involve the playback device 200 sending audio data toanother device or playback device on a network. In yet another example,the functions may involve pairing of the playback device 200 with one ormore playback devices to create a multi-channel audio environment.

Certain functions may involve the playback device 200 synchronizingplayback of audio content with one or more other playback devices.During synchronous playback, a listener will preferably not be able toperceive time-delay differences between playback of the audio content bythe playback device 200 and the one or more other playback devices. U.S.Pat. No. 8,234,395 entitled, “System and method for synchronizingoperations among a plurality of independently clocked digital dataprocessing devices,” which is hereby incorporated by reference, providesin more detail some examples for audio playback synchronization amongplayback devices.

The memory 206 may further be configured to store data associated withthe playback device 200, such as one or more zones and/or zone groupsthe playback device 200 is a part of, audio sources accessible by theplayback device 200, or a playback queue that the playback device 200(or some other playback device) may be associated with. The data may bestored as one or more state variables that are periodically updated andused to describe the state of the playback device 200. The memory 206may also include the data associated with the state of the other devicesof the media system, and shared from time to time among the devices sothat one or more of the devices have the most recent data associatedwith the system. Other embodiments are also possible.

The audio processing components 208 may include one or moredigital-to-analog converters (DAC), an audio preprocessing component, anaudio enhancement component or a digital signal processor (DSP), and soon. In one embodiment, one or more of the audio processing components208 may be a subcomponent of the processor 202. In one example, audiocontent may be processed and/or intentionally altered by the audioprocessing components 208 to produce audio signals. The produced audiosignals may then be provided to the audio amplifier(s) 210 foramplification and playback through speaker(s) 212. Particularly, theaudio amplifier(s) 210 may include devices configured to amplify audiosignals to a level for driving one or more of the speakers 212. Thespeaker(s) 212 may include an individual transducer (e.g., a “driver”)or a complete speaker system involving an enclosure with one or moredrivers. A particular driver of the speaker(s) 212 may include, forexample, a subwoofer (e.g., for low frequencies), a mid-range driver(e.g., for middle frequencies), and/or a tweeter (e.g., for highfrequencies). In some cases, each transducer in the one or more speakers212 may be driven by an individual corresponding audio amplifier of theaudio amplifier(s) 210. In addition to producing analog signals forplayback by the playback device 200, the audio processing components 208may be configured to process audio content to be sent to one or moreother playback devices for playback.

Audio content to be processed and/or played back by the playback device200 may be received from an external source, such as via an audioline-in input connection (e.g., an auto-detecting 3.5 mm audio line-inconnection) or the network interface 214.

The microphone(s) 220 may include an audio sensor configured to convertdetected sounds into electrical signals. The electrical signal may beprocessed by the audio processing components 208 and/or the processor202. The microphone(s) 220 may be positioned in one or more orientationsat one or more locations on the playback device 200. The microphone(s)220 may be configured to detect sound within one or more frequencyranges. In one case, one or more of the microphone(s) 220 may beconfigured to detect sound within a frequency range of audio that theplayback device 200 is capable or rendering. In another case, one ormore of the microphone(s) 220 may be configured to detect sound within afrequency range audible to humans. Other examples are also possible.

The network interface 214 may be configured to facilitate a data flowbetween the playback device 200 and one or more other devices on a datanetwork. As such, the playback device 200 may be configured to receiveaudio content over the data network from one or more other playbackdevices in communication with the playback device 200, network deviceswithin a local area network, or audio content sources over a wide areanetwork such as the Internet. In one example, the audio content andother signals transmitted and received by the playback device 200 may betransmitted in the form of digital packet data containing an InternetProtocol (IP)-based source address and IP-based destination addresses.In such a case, the network interface 214 may be configured to parse thedigital packet data such that the data destined for the playback device200 is properly received and processed by the playback device 200.

As shown, the network interface 214 may include wireless interface(s)216 and wired interface(s) 218. The wireless interface(s) 216 mayprovide network interface functions for the playback device 200 towirelessly communicate with other devices (e.g., other playbackdevice(s), speaker(s), receiver(s), network device(s), control device(s)within a data network the playback device 200 is associated with) inaccordance with a communication protocol (e.g., any wireless standardincluding IEEE 802.11a, 802.11b, 802.11g, 802.11n, 802.11ac, 802.15, 4Gmobile communication standard, and so on). The wired interface(s) 218may provide network interface functions for the playback device 200 tocommunicate over a wired connection with other devices in accordancewith a communication protocol (e.g., IEEE 802.3). While the networkinterface 214 shown in FIG. 2 includes both wireless interface(s) 216and wired interface(s) 218, the network interface 214 may in someembodiments include only wireless interface(s) or only wiredinterface(s).

In one example, the playback device 200 and one other playback devicemay be paired to play two separate audio components of audio content.For instance, playback device 200 may be configured to play a leftchannel audio component, while the other playback device may beconfigured to play a right channel audio component, thereby producing orenhancing a stereo effect of the audio content. The paired playbackdevices (also referred to as “bonded playback devices”) may further playaudio content in synchrony with other playback devices.

In another example, the playback device 200 may be sonicallyconsolidated with one or more other playback devices to form a single,consolidated playback device. A consolidated playback device may beconfigured to process and reproduce sound differently than anunconsolidated playback device or playback devices that are paired,because a consolidated playback device may have additional speakerdrivers through which audio content may be rendered. For instance, ifthe playback device 200 is a playback device designed to render lowfrequency range audio content (i.e. a subwoofer), the playback device200 may be consolidated with a playback device designed to render fullfrequency range audio content. In such a case, the full frequency rangeplayback device, when consolidated with the low frequency playbackdevice 200, may be configured to render only the mid and high frequencycomponents of audio content, while the low frequency range playbackdevice 200 renders the low frequency component of the audio content. Theconsolidated playback device may further be paired with a singleplayback device or yet another consolidated playback device.

By way of illustration, SONOS, Inc. presently offers (or has offered)for sale certain playback devices including a “PLAY:1,” “PLAY:3,”“PLAY:5,” “PLAYBAR,” “CONNECT:AMP,” “CONNECT,” and “SUB.” Any otherpast, present, and/or future playback devices may additionally oralternatively be used to implement the playback devices of exampleembodiments disclosed herein. Additionally, it is understood that aplayback device is not limited to the example illustrated in FIG. 2 orto the SONOS product offerings. For example, a playback device mayinclude a wired or wireless headphone. In another example, a playbackdevice may include or interact with a docking station for personalmobile media playback devices. In yet another example, a playback devicemay be integral to another device or component such as a television, alighting fixture, or some other device for indoor or outdoor use.

b. Example Playback Zone Configurations

Referring back to the media playback system 100 of FIG. 1 , theenvironment may have one or more playback zones, each with one or moreplayback devices. The media playback system 100 may be established withone or more playback zones, after which one or more zones may be added,or removed to arrive at the example configuration shown in FIG. 1 . Eachzone may be given a name according to a different room or space such asan office, bathroom, master bedroom, bedroom, kitchen, dining room,living room, and/or balcony. In one case, a single playback zone mayinclude multiple rooms or spaces. In another case, a single room orspace may include multiple playback zones.

As shown in FIG. 1 , the balcony, dining room, kitchen, bathroom,office, and bedroom zones each have one playback device, while theliving room and master bedroom zones each have multiple playbackdevices. In the living room zone, playback devices 104, 106, 108, and110 may be configured to play audio content in synchrony as individualplayback devices, as one or more bonded playback devices, as one or moreconsolidated playback devices, or any combination thereof. Similarly, inthe case of the master bedroom, playback devices 122 and 124 may beconfigured to play audio content in synchrony as individual playbackdevices, as a bonded playback device, or as a consolidated playbackdevice.

In one example, one or more playback zones in the environment of FIG. 1may each be playing different audio content. For instance, the user maybe grilling in the balcony zone and listening to hip hop music beingplayed by the playback device 102 while another user may be preparingfood in the kitchen zone and listening to classical music being playedby the playback device 114. In another example, a playback zone may playthe same audio content in synchrony with another playback zone. Forinstance, the user may be in the office zone where the playback device118 is playing the same rock music that is being played by playbackdevice 102 in the balcony zone. In such a case, playback devices 102 and118 may be playing the rock music in synchrony such that the user mayseamlessly (or at least substantially seamlessly) enjoy the audiocontent that is being played out-loud while moving between differentplayback zones. Synchronization among playback zones may be achieved ina manner similar to that of synchronization among playback devices, asdescribed in previously referenced U.S. Pat. No. 8,234,395.

As suggested above, the zone configurations of the media playback system100 may be dynamically modified, and in some embodiments, the mediaplayback system 100 supports numerous configurations. For instance, if auser physically moves one or more playback devices to or from a zone,the media playback system 100 may be reconfigured to accommodate thechange(s). For instance, if the user physically moves the playbackdevice 102 from the balcony zone to the office zone, the office zone maynow include both the playback device 118 and the playback device 102.The playback device 102 may be paired or grouped with the office zoneand/or renamed if so desired via a control device such as the controldevices 126 and 128. On the other hand, if the one or more playbackdevices are moved to a particular area in the home environment that isnot already a playback zone, a new playback zone may be created for theparticular area.

Further, different playback zones of the media playback system 100 maybe dynamically combined into zone groups or split up into individualplayback zones. For instance, the dining room zone and the kitchen zone114 may be combined into a zone group for a dinner party such thatplayback devices 112 and 114 may render audio content in synchrony. Onthe other hand, the living room zone may be split into a television zoneincluding playback device 104, and a listening zone including playbackdevices 106, 108, and 110, if the user wishes to listen to music in theliving room space while another user wishes to watch television.

c. Example Control Devices

FIG. 3 shows a functional block diagram of an example control device 300that may be configured to be one or both of the control devices 126 and128 of the media playback system 100. As shown, the control device 300may include a processor 302, memory 304, a network interface 306, and auser interface 308. In one example, the control device 300 may be adedicated controller for the media playback system 100. In anotherexample, the control device 300 may be a network device on which mediaplayback system controller application software may be installed, suchas for example, an iPhone™, iPad™ or any other smart phone, tablet ornetwork device (e.g., a networked computer such as a PC or Mac™)

The processor 302 may be configured to perform functions relevant tofacilitating user access, control, and configuration of the mediaplayback system 100. The memory 304 may be configured to storeinstructions executable by the processor 302 to perform those functions.The memory 304 may also be configured to store the media playback systemcontroller application software and other data associated with the mediaplayback system 100 and the user.

The microphone(s) 310 may include an audio sensor configured to convertdetected sounds into electrical signals. The electrical signal may beprocessed by the processor 302. In one case, if the control device 300is a device that may also be used as a means for voice communication orvoice recording, one or more of the microphone(s) 310 may be amicrophone for facilitating those functions. For instance, the one ormore of the microphone(s) 310 may be configured to detect sound within afrequency range that a human is capable of producing and/or a frequencyrange audible to humans. Other examples are also possible.

In one example, the network interface 306 may be based on an industrystandard (e.g., infrared, radio, wired standards including IEEE 802.3,wireless standards including IEEE 802.11a, 802.11b, 802.11g, 802.11n,802.11ac, 802.15, 4G mobile communication standard, and so on). Thenetwork interface 306 may provide a means for the control device 300 tocommunicate with other devices in the media playback system 100. In oneexample, data and information (e.g., such as a state variable) may becommunicated between control device 300 and other devices via thenetwork interface 306. For instance, playback zone and zone groupconfigurations in the media playback system 100 may be received by thecontrol device 300 from a playback device or another network device, ortransmitted by the control device 300 to another playback device ornetwork device via the network interface 306. In some cases, the othernetwork device may be another control device.

Playback device control commands such as volume control and audioplayback control may also be communicated from the control device 300 toa playback device via the network interface 306. As suggested above,changes to configurations of the media playback system 100 may also beperformed by a user using the control device 300. The configurationchanges may include adding/removing one or more playback devices to/froma zone, adding/removing one or more zones to/from a zone group, forminga bonded or consolidated player, separating one or more playback devicesfrom a bonded or consolidated player, among others. Accordingly, thecontrol device 300 may sometimes be referred to as a controller, whetherthe control device 300 is a dedicated controller or a network device onwhich media playback system controller application software isinstalled.

The user interface 308 of the control device 300 may be configured tofacilitate user access and control of the media playback system 100, byproviding a controller interface such as the controller interface 400shown in FIG. 4 . The controller interface 400 includes a playbackcontrol region 410, a playback zone region 420, a playback status region430, a playback queue region 440, and an audio content sources region450. The user interface 400 as shown is just one example of a userinterface that may be provided on a network device such as the controldevice 300 of FIG. 3 (and/or the control devices 126 and 128 of FIG. 1 )and accessed by users to control a media playback system such as themedia playback system 100. Other user interfaces of varying formats,styles, and interactive sequences may alternatively be implemented onone or more network devices to provide comparable control access to amedia playback system.

The playback control region 410 may include selectable (e.g., by way oftouch or by using a cursor) icons to cause playback devices in aselected playback zone or zone group to play or pause, fast forward,rewind, skip to next, skip to previous, enter/exit shuffle mode,enter/exit repeat mode, enter/exit cross fade mode. The playback controlregion 410 may also include selectable icons to modify equalizationsettings, and playback volume, among other possibilities.

The playback zone region 420 may include representations of playbackzones within the media playback system 100. In some embodiments, thegraphical representations of playback zones may be selectable to bringup additional selectable icons to manage or configure the playback zonesin the media playback system, such as a creation of bonded zones,creation of zone groups, separation of zone groups, and renaming of zonegroups, among other possibilities.

For example, as shown, a “group” icon may be provided within each of thegraphical representations of playback zones. The “group” icon providedwithin a graphical representation of a particular zone may be selectableto bring up options to select one or more other zones in the mediaplayback system to be grouped with the particular zone. Once grouped,playback devices in the zones that have been grouped with the particularzone will be configured to play audio content in synchrony with theplayback device(s) in the particular zone. Analogously, a “group” iconmay be provided within a graphical representation of a zone group. Inthis case, the “group” icon may be selectable to bring up options todeselect one or more zones in the zone group to be removed from the zonegroup. Other interactions and implementations for grouping andungrouping zones via a user interface such as the user interface 400 arealso possible. The representations of playback zones in the playbackzone region 420 may be dynamically updated as playback zone or zonegroup configurations are modified.

The playback status region 430 may include graphical representations ofaudio content that is presently being played, previously played, orscheduled to play next in the selected playback zone or zone group. Theselected playback zone or zone group may be visually distinguished onthe user interface, such as within the playback zone region 420 and/orthe playback status region 430. The graphical representations mayinclude track title, artist name, album name, album year, track length,and other relevant information that may be useful for the user to knowwhen controlling the media playback system via the user interface 400.

The playback queue region 440 may include graphical representations ofaudio content in a playback queue associated with the selected playbackzone or zone group. In some embodiments, each playback zone or zonegroup may be associated with a playback queue containing informationcorresponding to zero or more audio items for playback by the playbackzone or zone group. For instance, each audio item in the playback queuemay comprise a uniform resource identifier (URI), a uniform resourcelocator (URL) or some other identifier that may be used by a playbackdevice in the playback zone or zone group to find and/or retrieve theaudio item from a local audio content source or a networked audiocontent source, possibly for playback by the playback device.

In one example, a playlist may be added to a playback queue, in whichcase information corresponding to each audio item in the playlist may beadded to the playback queue. In another example, audio items in aplayback queue may be saved as a playlist. In a further example, aplayback queue may be empty, or populated but “not in use” when theplayback zone or zone group is playing continuously streaming audiocontent, such as Internet radio that may continue to play untilotherwise stopped, rather than discrete audio items that have playbackdurations. In an alternative embodiment, a playback queue can includeInternet radio and/or other streaming audio content items and be “inuse” when the playback zone or zone group is playing those items. Otherexamples are also possible.

When playback zones or zone groups are “grouped” or “ungrouped,”playback queues associated with the affected playback zones or zonegroups may be cleared or re-associated. For example, if a first playbackzone including a first playback queue is grouped with a second playbackzone including a second playback queue, the established zone group mayhave an associated playback queue that is initially empty, that containsaudio items from the first playback queue (such as if the secondplayback zone was added to the first playback zone), that contains audioitems from the second playback queue (such as if the first playback zonewas added to the second playback zone), or a combination of audio itemsfrom both the first and second playback queues. Subsequently, if theestablished zone group is ungrouped, the resulting first playback zonemay be re-associated with the previous first playback queue, or beassociated with a new playback queue that is empty or contains audioitems from the playback queue associated with the established zone groupbefore the established zone group was ungrouped. Similarly, theresulting second playback zone may be re-associated with the previoussecond playback queue, or be associated with a new playback queue thatis empty, or contains audio items from the playback queue associatedwith the established zone group before the established zone group wasungrouped. Other examples are also possible.

Referring back to the user interface 400 of FIG. 4 , the graphicalrepresentations of audio content in the playback queue region 440 mayinclude track titles, artist names, track lengths, and other relevantinformation associated with the audio content in the playback queue. Inone example, graphical representations of audio content may beselectable to bring up additional selectable icons to manage and/ormanipulate the playback queue and/or audio content represented in theplayback queue. For instance, a represented audio content may be removedfrom the playback queue, moved to a different position within theplayback queue, or selected to be played immediately, or after anycurrently playing audio content, among other possibilities. A playbackqueue associated with a playback zone or zone group may be stored in amemory on one or more playback devices in the playback zone or zonegroup, on a playback device that is not in the playback zone or zonegroup, and/or some other designated device.

The audio content sources region 450 may include graphicalrepresentations of selectable audio content sources from which audiocontent may be retrieved and played by the selected playback zone orzone group. Discussions pertaining to audio content sources may be foundin the following section.

d. Example Audio Content Sources

As indicated previously, one or more playback devices in a zone or zonegroup may be configured to retrieve for playback audio content (e.g.according to a corresponding URI or URL for the audio content) from avariety of available audio content sources. In one example, audiocontent may be retrieved by a playback device directly from acorresponding audio content source (e.g., a line-in connection). Inanother example, audio content may be provided to a playback device overa network via one or more other playback devices or network devices.

Example audio content sources may include a memory of one or moreplayback devices in a media playback system such as the media playbacksystem 100 of FIG. 1 , local music libraries on one or more networkdevices (such as a control device, a network-enabled personal computer,or a networked-attached storage (NAS), for example), streaming audioservices providing audio content via the Internet (e.g., the cloud), oraudio sources connected to the media playback system via a line-in inputconnection on a playback device or network devise, among otherpossibilities.

In some embodiments, audio content sources may be regularly added orremoved from a media playback system such as the media playback system100 of FIG. 1 . In one example, an indexing of audio items may beperformed whenever one or more audio content sources are added, removedor updated. Indexing of audio items may involve scanning foridentifiable audio items in all folders/directory shared over a networkaccessible by playback devices in the media playback system, andgenerating or updating an audio content database containing metadata(e.g., title, artist, album, track length, among others) and otherassociated information, such as a URI or URL for each identifiable audioitem found. Other examples for managing and maintaining audio contentsources may also be possible.

The above discussions relating to playback devices, controller devices,playback zone configurations, and media content sources provide onlysome examples of operating environments within which functions andmethods described below may be implemented. Other operating environmentsand configurations of media playback systems, playback devices, andnetwork devices not explicitly described herein may also be applicableand suitable for implementation of the functions and methods.

III. Example Methods Related to Synchronized Audio Mixing

As discussed above, some examples described herein involve, among otherthings, a first playback device (i) playing a first audio stream whilealso (ii) playing a second audio stream in synchrony with a secondplayback device. The first and second playback devices may both accesscommon timing information that facilitates synchronous playback of thesecond audio stream by the first and second playback devices. Otheraspects of the examples will be made apparent in the remainder of thedescription herein.

Method 500 shown in FIG. 5 presents an example method that can beimplemented within an operating environment involving, for example, themedia playback system 100 of FIG. 1 , one or more of the playback device200 of FIG. 2 , and one or more of the control device 300 of FIG. 3 .Method 500 may include one or more operations, functions, or actions asillustrated by one or more of blocks 502 and 504. Although the blocksare illustrated in sequential order, these blocks may also be performedin parallel, and/or in a different order than those described herein.Also, the various blocks may be combined into fewer blocks, divided intoadditional blocks, and/or removed based upon the desired implementation.

In addition, for the method 500 and other processes and methodsdisclosed herein, the flowchart shows functionality and operation of onepossible implementation of present embodiments. In this regard, eachblock may represent a module, a segment, or a portion of program code,which includes one or more instructions executable by a processor forimplementing specific logical functions or steps in the process. Theprogram code may be stored on any type of computer-readable medium, forexample, such as a storage device including a disk or hard drive. Thecomputer-readable medium may include non-transitory computer-readablemedium, for example, such as computer-readable media that stores datafor short periods of time like register memory, processor cache, andRandom Access Memory (RAM). The computer-readable medium may alsoinclude non-transitory media, such as secondary or persistent long-termstorage, like read-only memory (ROM), optical or magnetic disks,compact-disc read-only memory (CD-ROM), for example. Thecomputer-readable media may also be any other volatile or non-volatilestorage systems. The computer-readable medium may be considered acomputer-readable storage medium, for example, or a tangible storagedevice. In addition, for the method 500 and other processes and methodsdisclosed herein, each block in FIG. 5 may represent circuitry that iswired to perform the specific logical functions in the process.

At block 502, the method 500 involves generating, by a first playbackdevice, a mixed audio signal comprising one or more components of afirst audio stream and one or more components of a second audio stream.Referring to FIG. 6 as an example, a playback device 602 may receive (orotherwise access) an audio stream 604 and an audio stream 606. Theplayback device 602 may use the audio stream 604 and the audio stream606 to generate a mixed audio signal 616 that includes components of theaudio stream 604 and components of the audio stream 606. The playbackdevice 602 may provide the mixed audio signal 616 to one or morespeakers of the playback device 602.

In some examples, the playback device 602 may provide the mixed audiosignal 616 to a digital-to-analog converter (DAC) (not shown) forconverting the mixed audio signal 616 to an analog signal. For example,the DAC may provide the analog signal to one or more speakers that areintegrated within the playback device 602. In another example, the DACmay provide the analog signal via one or more line out connections toone or more external speakers. In other examples, the external speakersmay include integrated DACs and the mixed audio signal 616 may beprovided directly to the external speakers by the playback device 602.The playback device 608 may perform similar operations with the audiosignal 618.

In some examples, generating the mixed audio signal may include, foreach time of a set of sample times, determining a respective sum of (i)a first sample of the first audio stream that corresponds to the givensample time and (ii) a second sample of the second audio stream thatcorresponds to the given sample time. For instance, the first audiostream 604 may comprise data packets that include a collection ofsamples that digitally quantize a waveform that embodies the first audiostream 604. The second audio stream 606 may similarly comprise datapackets that include a different collection of samples that digitallyquantize a waveform that embodies the second audio stream 606.

Referring to FIG. 7 , for example, the audio stream 604 may include acollection of 8-bit values (e.g., corresponding to a decimal range of−128−127) that quantize the waveform of audio stream 604 at “n”respective times T₀, T₁, T₂, T₃, T₄, . . . and T_(n). (Audio streamshaving bit depths other than 8-bit, such as 16-bit, are also possible.)The audio stream 606 may similarly include a collection of 8-bit valuesthat quantize the waveform of the audio stream 606 at the respectivetimes T₀, T₁, T₂, T₃, T₄, . . . and T_(n). Purely by way of example, “n”may be equal to 128. This would mean that the playback device 602generates the mixed audio signal 616 128 samples at a time. Assuming asample rate of 44.1 kHz (other examples are possible), the playbackdevice 602 may generate a new 128-sample portion of the mixed audiosignal 616 approximately every 3 milliseconds.

As shown in FIG. 7 , the mixed audio signal 616 may be generated (atleast initially) as a “raw” audio signal 617. For example, the playbackdevice 602 may determine sums of the audio streams 604 and 606 at therespective times T₀, T₁, T₂, T₃, T₄, . . . and T_(n). At T₀, the sum ofthe audio streams 604 and 606 may be equal to 175 (55+120). At T₁, thesum of the audio streams 604 and 606 may be equal to −180 (−60−120). AtT₂, the sum of the audio streams 604 and 606 may be equal to 50(−65+115). At T₃, the sum of the audio streams 604 and 606 may be equalto −40 (70−110). At T₄, the sum of the audio streams 604 and 606 may beequal to 35 (−75+110). At T_(n), the sum of the audio streams 604 and606 may be equal to −185 (−85−100). In situations where each of thevalues of the raw audio signal 617 respectively corresponding to thetimes T₀, T₁, T₂, T₃, T₄, . . . and T_(n), is within the dynamic rangeof the playback device 602 (e.g., −128−127) the mixed audio signal 616played by the playback device 602 may be equal to the raw audio signalshown 617.

Generating the mixed audio signal may further include determining that aparticular sum corresponding to a particular sample time of the set ofsample times is outside of a dynamic range of the first playback device;and generating a sample of the mixed audio signal that corresponds tothe particular time, where the generated sample is within the dynamicrange of the first playback device. For example, the playback device 602may determine that the sum “175” of the raw audio signal 617corresponding to T₀ is greater than an upper limit (e.g., 127) of thedynamic range of the playback device 602. The playback device 602 maythen generate a sample of a “clipped” audio signal 619 having a value of127 corresponding to T₀. In some examples, the playback device 602 maygenerate a sample for the clipped audio signal 619 having a value (e.g.,120) that is within, but does not correspond to a limit of, the dynamicrange of the playback device 602. When one or more values of the rawaudio signal 617 fall outside of the dynamic range of the playbackdevice 602, the clipped audio signal 619 depicted in FIG. 7 may be usedas the mixed audio signal 616.

By further example, the playback device 602 may determine that the sum−180 of the raw audio signal 617 corresponding to T₁ is less than alower limit (e.g., −128) of the dynamic range of the playback device602. The playback device 602 may then generate a sample of the clippedaudio signal 619 having a value of −128 corresponding to T₁. Thisprocess of identifying values of the raw audio signal 617 that falloutside of the dynamic range of the playback device 602 and replacingthe identified values with values corresponding to the upper or lowerlimit of the dynamic range may be referred to as “clipping.” Clippingmay preserve loudness of audio output while introducing some degree ofsignal distortion. Clipping may be useful when values of the raw audiosignal 617 only occasionally exceed the dynamic range of the playbackdevice 602.

Generating the mixed audio signal may further include determining that aparticular sum corresponding to a particular sample time of the set ofsample times is outside of a dynamic range of the first playback device;determining a scaling factor; and for each of the sample times of theset of sample times, scaling the sum corresponding to the given sampletime by the scaling factor. For example, the playback device 602 maydetermine that the sum “−185” corresponding to T_(n) may have thelargest magnitude of any sample of the raw audio signal 617. Theplayback device 602 may then determine a scaling factor that, whenapplied to all values of the raw audio signal 617, yields valuesrespectively corresponding to each of the times T₀, T₁, T₂, T₃, T₄, . .. and T_(n) that are all within the dynamic range (e.g., −128−127) ofthe playback device 602.

As shown in FIG. 7 , the playback device 602 may multiply the values ofthe raw audio signal 617 by a scaling factor of approximately 0.692(−128/−185) to yield respective values of a scaled audio signal 621. Forexample, the sum 175 corresponding to T₀ scales to 121 (175*0.692), thesum −180 corresponding to T₁ scales to −125 (−125*0.692), the sum 50corresponding to T₂ scales to 35 (50*0.692), the sum −40 correspondingto T₃ scales to −28 (−40*0.692), the sum 35 corresponding to T₄ scalesto 24 (35*0.692), and the sum −185 corresponding to T_(n) scales to−128. Scaling a raw audio signal to generate a mixed audio signal may beuseful when the raw audio signal often exceeds the dynamic range of theplayback device. In this context, the scaled audio signal 621 depictedin FIG. 7 may be used as the mixed audio signal 616.

In some examples, the mixed audio signal comprises (i) a first portionof the first audio stream that fades out as the mixed audio signal isplayed and (ii) a portion of the second audio stream that fades in asthe mixed audio signal is played. In other examples, the mixed audiosignal comprises (i) a portion of the first audio stream that fades inas the mixed audio signal is played and (ii) a portion of the secondaudio stream that fades out as the mixed audio signal is played. Thesemethods may involve generating a “crossfaded” mixed audio signal byapplying a fade-in gain curve or a fade-out gain curve respectively tothe first audio stream and the second audio stream, as appropriate. Anexample fade-in gain curve 802 and an example fade-out gain curve 804are shown in FIG. 8 .

Referring to FIG. 6 , a playback device 608 may also receive (orotherwise access) the audio stream 606 and, in some examples, an audiostream 610. The playback device 608 may play an audio signal 618 that insome examples may be equivalent to the audio stream 606, but in otherexamples may be a mixed audio signal generated by the playback device608 to include components of both audio streams 606 and 610. The audiostream 610 may be equivalent to the audio stream 604, but in otherexamples may be an audio stream different from the audio stream 604. Theplayback device 608 may play the audio stream 610 in synchrony withanother playback device, such as playback device 624. The playbackdevice 608 need not (but could) play audio stream 610 in synchrony withthe playback device 602 playing audio stream 604.

At block 504, the method 500 involves playing, by the first playbackdevice, the mixed audio signal, where the one or more components of thesecond audio stream of the mixed audio signal played by the firstplayback device are played in synchrony with a second playback deviceconfigured to play the second audio stream. For example, the playbackdevice 602 may play the mixed audio signal 616 as the playback device608 plays the audio signal 618, such that the components of the audiostream 606 played by the playback device 602 are played in synchronywith the components of the audio stream 606 played by the playbackdevice 608.

In some examples, the first playback device 602 playing the componentsof the audio stream 606 in synchrony with the playback device 608 maymean that, at any given time, the playback device 602 and the playbackdevice 608 are playing the same component of the audio stream 606. Inother examples, the playback device 602 may play the audio stream 606with a predetermined or perhaps dynamically calculated delay time orlead time when compared to the playback device 608 playing the audiostream 606. In this context, playing the audio stream 606 in “synchrony”means that there may be a predetermined or perhaps dynamicallycalculated lead time or delay time (possibly zero) between the playbackdevices 602 and 608 playing a given component of the audio stream 606.Descriptions of multiple playback devices playing one or more audiostreams in synchrony may be found within U.S. Pat. No. 8,234,395, whichis hereby incorporated by reference. Such disclosure may be found, forexample and without limitation, at col. 9 through col. 36.

Further operations related to the method 500 may involve receivingtiming information from a third playback device, where playing the mixedaudio signal comprises playing the mixed audio signal at a time based onthe timing information. For example, the playback device 602 may receivetiming information 626 from a playback device 624. The playback device608 may receive timing information 628 (which could be the same astiming information 626) from the playback device 624. The timinginformation 626 and 628 may each include a timestamp (e.g., indicatingrespective times to initiate playback of the audio stream 606), or thelike, that the playback devices 602 and 608 may respectively use, incoordination with respective clocks of the playback devices 602 and 608,to play the components of the audio stream 606 in synchrony.

Similarly, in instances where the playback device 608 is playing audiostream 610 in synchrony with an additional playback device (e.g.,playback device 624) playing audio stream 610, the playback device 608may receive timing information for playback of audio stream 610 from theadditional playback device and may receive timing information forplayback of audio stream 606 from playback device 602. Other examplesare possible.

Further operations related to the method 500 may involve receivingtiming information from the second playback device, where playing themixed audio signal comprises playing the mixed audio signal at a timebased on the timing information. For example, the playback device 602may receive timing information 612 from the playback device 608. Thetiming information 612 may include a timestamp (e.g., indicating a timeto initiate playback of the audio stream 606), or the like, that theplayback devices 602 and 608 may use, in coordination with respectiveclocks of the playback devices 602 and 608, to play the components ofthe audio stream 606 in synchrony.

Further operations related to the method 500 may involve sending timinginformation to the second playback device, where the first playbackdevice and the second playback device play the second audio stream insynchrony based on the timing information. For example, the playbackdevice 602 may send timing information 614 to the playback device 608.The timing information 614 may include a timestamp (e.g., indicating atime to initiate playback of the audio stream 606), or the like, thatthe playback devices 602 and 608 may use, in coordination withrespective clocks of the playback devices 602 and 608, to play thecomponents of the audio stream 606 in synchrony.

Further operations related to the method 500 may involve playing thefirst audio stream; receiving a command to fade out the first audiostream and fade in the second audio stream; and generating the mixedaudio signal based on receiving the command, where the mixed audiosignal comprises (i) a portion of the first audio stream that fades outas the mixed audio signal is played and (ii) a portion of the secondaudio stream that fades in as the mixed audio signal is played. Forexample, the playback device 602 may (i) play the audio stream 604, (ii)receive a command 622 from a control device 620 (or another device) tofade out the audio stream 604 and fade in the audio stream 606, and(iii) generate the mixed audio signal 616 based on receiving the command622. In this context, the mixed audio signal 616 may include a portionof the audio stream 604 that fades out as the mixed audio signal 616 isplayed and a portion of the audio stream 606 that fades in as the mixedaudio signal 616 is played.

For instance, the command 622 may relate to a command to “skip” fromplaying the audio stream 604 to playing the audio stream 606. With a“cross-fade” setting enabled at the playback device 602, such a commandmay implicitly include a command to fade out the audio stream 604 andfade in the audio stream 606, while playing the audio stream 606 insynchrony with the playback device 608.

Further operations related to the method 500 may involve playing thesecond audio stream; receiving a command to fade out the second audiostream and fade in the first audio stream; and generating the mixedaudio signal based on receiving the command, where the mixed audiosignal comprises (i) a portion of the first audio stream that fades inas the mixed audio signal is played and (ii) a portion of the secondaudio stream that fades out as the mixed audio signal is played. Forexample, the playback device 602 may (i) play the audio stream 606, (ii)receive a command 622 from the control device 620 (or another device) tofade out the audio stream 606 and fade in the audio stream 604, and(iii) generate the mixed audio signal 616 based on receiving the command622. In this context, the mixed audio signal 616 may include a portionof the audio stream 604 that fades in as the mixed audio signal 616 isplayed and a portion of the audio stream 606 that fades out as the mixedaudio signal 616 is played.

For instance, the command 622 may correspond with a command to “skip”from playing the audio stream 606 to playing the audio stream 604. Witha “cross-fade” setting enabled at the playback device 602, such acommand may implicitly include a command to fade out the audio stream606 and fade in the audio stream 604, while playing the audio stream 606in synchrony with the playback device 608.

In some examples, the second audio stream follows the first audio streamin a playback queue of the first playback device. In this context,further operations related to the method 500 may involve playing thefirst audio stream; determining that playback of the first audio streamwill be completed within a threshold duration of time; and generatingthe mixed audio signal in response to determining that playback of thefirst audio stream will be completed within the threshold duration oftime.

For instance, the audio stream 606 may follow the audio stream 604 in aplayback queue of the playback device 602. The playback device 602 may(i) play the audio stream 604, (ii) determine that playback of the audiostream 604 will be completed within a threshold duration of time (e.g.,ten seconds), and (iii) generate the mixed audio signal 616 in responseto determining that playback of the audio stream 604 will be completedwithin the threshold duration of time. That is, the playback device 602may be configured to automatically cross-fade from the audio stream 604to the audio stream 606 as the playback device 602 transitions fromplaying the audio stream 604 to playing the audio stream 606.

In other examples, the first audio stream follows the second audiostream in a playback queue of the first playback device. In thiscontext, further operations related to the method 500 may involveplaying the second audio stream; determining that playback of the secondaudio stream will be completed within a threshold duration of time; andgenerating the mixed audio signal in response to determining that thesecond audio stream will be completed within the threshold duration oftime.

For instance, the audio stream 604 may follow the audio stream 606 in aplayback queue of the playback device 602. The playback device 602 may(i) play the audio stream 606, (ii) determine that playback of the audiostream 606 will be completed within a threshold duration of time (e.g.,ten seconds), and (iii) generate the mixed audio signal 616 in responseto determining that playback of the audio stream 606 will be completedwithin the threshold duration of time. That is, the playback device 602may be configured to automatically cross-fade from the audio stream 606to the audio stream 604 as the playback device 602 transitions fromplaying the audio stream 606 to playing the audio stream 604.

In some examples, the first audio stream corresponds to a first channelof multi-channel audio content and the second audio stream correspondsto a second channel of the multi-channel audio content. For example, theaudio stream 604 may correspond to a front-left channel of 5.1-channelaudio content that includes front-left, front-center, front-right,rear-left, rear-right, and subwoofer channels. The playback device 602may correspond to a front-left speaker in a 4.1-channel audio systemthat includes front-left, front-right, rear-left, rear-right, andsubwoofer channels (but not a front-center channel). The audio stream606 may correspond to the center-front channel of the 5.1-channel audiocontent and it may be useful to mix the audio stream 606 with the audiostream 604 at the playback device 602 so that the playback device 602may play the front-center audio channel in duplicate with the playbackdevice 608 (which may correspond to the front-right channel of the4.1-channel audio system).

In other examples, the first audio stream corresponds to a channel ofmulti-channel audio content and the second audio stream is monauralaudio content. For instance, the playback device 602 may correspond to aleft channel of a stereo pair and the playback device 608 may correspondto a right channel of the stereo pair. As the playback device 602 playsa left channel of audio (e.g., the audio stream 604) and the playbackdevice 608 plays a right channel of audio (e.g., the audio stream 610),it may be useful for the playback devices 602 and 608 to play a monauralaudio stream (e.g., the audio stream 606) in synchrony.

IV. CONCLUSION

The description above discloses, among other things, various examplesystems, methods, apparatus, and articles of manufacture including,among other components, firmware and/or software executed on hardware.It is understood that such examples are merely illustrative and shouldnot be considered as limiting. For example, it is contemplated that anyor all of the firmware, hardware, and/or software aspects or componentscan be embodied exclusively in hardware, exclusively in software,exclusively in firmware, or in any combination of hardware, software,and/or firmware. Accordingly, the examples provided are not the onlyway(s) to implement such systems, methods, apparatus, and/or articles ofmanufacture.

Examples described herein involve, among other things, a first playbackdevice (i) playing a first audio stream while also (ii) playing a secondaudio stream in synchrony with a second playback device. The first andsecond playback devices may both access common timing information thatfacilitates synchronous playback of the second audio stream by the firstand second playback devices. Other aspects of the examples will be madeapparent in the remainder of the description herein.

In one aspect, a first example playback device includes one or moreprocessors and a non-transitory computer-readable medium storinginstructions that, when executed by the one or more processors, causethe first playback device to perform functions. The functions includegenerating a mixed audio signal comprising one or more components of afirst audio stream and one or more components of a second audio stream;and playing the mixed audio signal, where the one or more components ofthe second audio stream of the mixed audio signal played by the firstplayback device are played in synchrony with a second playback deviceconfigured to play the second audio stream.

In yet another aspect, an example non-transitory computer-readablemedium stores instructions that, when executed by a first playbackdevice, cause the first playback device to perform functions. Thefunctions include generating a mixed audio signal comprising one or morecomponents of a first audio stream and one or more components of asecond audio stream; and playing the mixed audio signal, where the oneor more components of the second audio stream of the mixed audio signalplayed by the first playback device are played in synchrony with asecond playback device configured to play the second audio stream.

In yet another aspect, an example method includes generating, by a firstplayback device, a mixed audio signal comprising one or more componentsof a first audio stream and one or more components of a second audiostream; and playing, by the first playback device, the mixed audiosignal, where the one or more components of the second audio stream ofthe mixed audio signal played by the first playback device are played insynchrony with a second playback device configured to play the secondaudio stream.

Additionally, references herein to “embodiment” means that a particularfeature, structure, or characteristic described in connection with theembodiment can be included in at least one example embodiment of aninvention. The appearances of this phrase in various places in thespecification are not necessarily all referring to the same embodiment,nor are separate or alternative embodiments mutually exclusive of otherembodiments. As such, the embodiments described herein, explicitly andimplicitly understood by one skilled in the art, can be combined withother embodiments.

The specification is presented largely in terms of illustrativeenvironments, systems, procedures, steps, logic blocks, processing, andother symbolic representations that directly or indirectly resemble theoperations of data processing devices coupled to networks. These processdescriptions and representations are typically used by those skilled inthe art to most effectively convey the substance of their work to othersskilled in the art. Numerous specific details are set forth to provide athorough understanding of the present disclosure. However, it isunderstood to those skilled in the art that certain embodiments of thepresent disclosure can be practiced without certain, specific details.In other instances, well known methods, procedures, components, andcircuitry have not been described in detail to avoid unnecessarilyobscuring aspects of the embodiments. Accordingly, the scope of thepresent disclosure is defined by the appended claims rather than theforgoing description of embodiments.

When any of the appended claims are read to cover a purely softwareand/or firmware implementation, at least one of the elements in at leastone example is hereby expressly defined to include a tangible,non-transitory medium such as a memory, DVD, CD, Blu-ray, and so on,storing the software and/or firmware.

1. A media playback system comprising: a first playback devicecomprising at least one first audio transducer, a first networkinterface, and a first housing carrying the at least one first audiotransducer and the first network interface; a second playback devicecomprising at least one second audio transducer, a second networkinterface, and a second housing carrying the at least one second audiotransducer and the second network interface; at least one processor; anddata storage including instructions that are executable by the at leastone processor such that the media playback system is configured to:receive audio content; play back, via the at least one first audiotransducer, at least one first audio signal representing at least afirst portion of the audio content; play back, via the at least onesecond audio transducer, at least second audio signal representing atleast a second portion of the audio content in synchrony with playbackof the at least one first audio signal on the first playback device;receive additional audio content; generate at least one third audiosignal representing at least the first portion of the audio content andthe additional audio content, wherein the instructions that areexecutable by the at least one processor such that the media playbacksystem is configured to generate the at least one third audio signalcomprise instructions that are executable by the at least one processorsuch that the media playback system is configured to mix the firstportion of the audio content with the additional audio content; generateat least one fourth audio signal representing at least the secondportion of the audio content and the additional audio content, whereinthe instructions that are executable by the at least one processor suchthat the media playback system is configured to generate the at leastone fourth audio signal comprise instructions that are executable by theat least one processor such that the media playback system is configuredto mix the second portion of the audio content with the additional audiocontent; play back the at least one third audio signal via the at leastone first audio transducer; and play back the at least one fourth audiosignal via the at least one second audio transducer in synchrony withplayback of the at least one third audio signal on the first playbackdevice.
 2. The media playback system of claim 1, wherein the audiocontent comprises a first channel and a second channel of multi-channelaudio, wherein the additional audio content comprises a center channelof the multi-channel audio, wherein the instructions that are executableby the at least one processor such that the media playback system isconfigured to mix the first portion of the audio content with theadditional audio content comprise instructions that are executable bythe at least one processor such that the media playback system isconfigured to mix the first channel and the center channel, and whereinthe instructions that are executable by the at least one processor suchthat the media playback system is configured to mix the second portionof the audio content with the additional audio content compriseinstructions that are executable by the at least one processor such thatthe media playback system is configured to mix the second channel andthe center channel.
 3. The media playback system of claim 2, wherein thefirst playback device comprises a high-definition multimedia interface(HDMI) port, and wherein the instructions that are executable by the atleast one processor such that the media playback system is configured toreceive the additional audio content comprise instructions that areexecutable by the at least one processor such that the media playbacksystem is configured to receive the additional audio content via theHDMI port.
 4. The media playback system of claim 1, wherein the audiocontent comprises a first channel and a second channel of multi-channelaudio, wherein the additional audio content comprises an audionotification, wherein the instructions that are executable by the atleast one processor such that the media playback system is configured tomix the first portion of the audio content with the additional audiocontent comprise instructions that are executable by the at least oneprocessor such that the media playback system is configured to mix thefirst channel and the audio notification, and wherein the instructionsthat are executable by the at least one processor such that the mediaplayback system is configured to mix the second portion of the audiocontent with the additional audio content comprise instructions that areexecutable by the at least one processor such that the media playbacksystem is configured to mix the second channel and the audionotification.
 5. The media playback system of claim 4, wherein the firstplayback device comprises a high-definition multimedia interface (HDMI)port, wherein the instructions that are executable by the at least oneprocessor such that the media playback system is configured to receivethe audio content comprise instructions that are executable by the atleast one processor such that the media playback system is configured toreceive the audio content via the HDMI port, and wherein theinstructions that are executable by the at least one processor such thatthe media playback system is configured to receive the additional audiocontent comprise instructions that are executable by the at least oneprocessor such that the media playback system is configured to receivethe additional audio content via the first network interface.
 6. Themedia playback system of claim 1, wherein the first housing of the firstplayback device is configured for out-loud playback, wherein the secondhousing of the second playback device is formed into headphones, andwherein the at least one second audio transducer comprises multipleaudio transducers carried by the headphones.
 7. The media playbacksystem of claim 6, wherein the instructions are executable by the atleast one processor such that the media playback system is furtherconfigured to: determine that particular samples of the at least onefourth audio signal exceed a first threshold level; and reduce levels ofthe particular samples below the first threshold level.
 8. The mediaplayback system of claim 7, wherein the instructions are executable bythe at least one processor such that the media playback system isfurther configured to: determine that particular samples of the at leastone third audio signal exceed a second threshold level that is higherthan the first threshold level; and reduce levels of the particularsamples below the second threshold level.
 9. The media playback systemof claim 8, wherein the instructions that are executable by the at leastone processor such that the media playback system is configured toreduce levels of the particular samples below the first threshold levelcomprise instructions that are executable by the at least one processorsuch that the media playback system is configured to: apply at least onescaling factor to the particular samples of the at least one fourthaudio signal.
 10. The media playback system of claim 1, wherein the atleast one processor comprises a first processor that is carried in thefirst housing and a second processor that is carried in the secondhousing, and wherein the instructions that are executable by the atleast one processor such that the media playback system is configured tomix the first portion of the audio content with the additional audiocontent comprise instructions that are executable by the at least oneprocessor such that the media playback system is configured to mix thefirst portion of the audio content with the additional audio content viathe first processor, and wherein the instructions that are executable bythe at least one processor such that the media playback system isconfigured to mix the second portion of the audio content with theadditional audio content comprise instructions that are executable bythe at least one processor such that the media playback system isconfigured to mix the second portion of the audio content with theadditional audio content via the second processor.
 11. The mediaplayback system of claim 1, wherein the instructions are executable bythe at least one processor such that the media playback system isfurther configured to: send, via the first network interface to thesecond playback device, the at least one second audio signalrepresenting at least a second portion of the audio content; andreceive, via the second network interface, the at least one second audiosignal.
 12. The media playback system of claim 11, wherein theinstructions are executable by the at least one processor such that themedia playback system is further configured to: send, via the firstnetwork interface to the second playback device, the at least one fourthaudio signal representing at least a second portion of the audiocontent; and receive, via the second network interface, the at least onefourth audio signal.
 13. A method to be performed by a media playbacksystem comprising a first playback device and a second playback device,the method comprising: receiving audio content; playing back, via atleast one first audio transducer, at least one first audio signalrepresenting at least a first portion of the audio content, wherein thefirst playback device comprises the at least one first audio transducerand a first housing carrying the at least one first audio transducer;playing back, via at least one second audio transducer, at least secondaudio signal representing at least a second portion of the audio contentin synchrony with playback of the at least one first audio signal on thefirst playback device, wherein the second playback device comprises theat least one second audio transducer and a second housing carrying theat least one second audio transducer; receiving additional audiocontent; generating at least one third audio signal representing atleast the first portion of the audio content and the additional audiocontent, wherein generating the at least one third audio signalcomprises mixing the first portion of the audio content with theadditional audio content; generating at least one fourth audio signalrepresenting at least the second portion of the audio content and theadditional audio content, wherein generating the at least one fourthaudio signal comprises mixing the second portion of the audio contentwith the additional audio content; playing back the at least one thirdaudio signal via the at least one first audio transducer; and playingback the at least one fourth audio signal via the at least one secondaudio transducer in synchrony with playback of the at least one thirdaudio signal on the first playback device.
 14. The method of claim 13,wherein the audio content comprises a first channel and a second channelof multi-channel audio, wherein the additional audio content comprises acenter channel of the multi-channel audio, wherein mixing the firstportion of the audio content with the additional audio content comprisesmixing the first channel and the center channel, and wherein mixing thesecond portion of the audio content with the additional audio contentcomprises mixing the second channel and the center channel.
 15. Themethod of claim 13, wherein the audio content comprises a first channeland a second channel of multi-channel audio, wherein the additionalaudio content comprises an audio notification, wherein mixing the firstportion of the audio content with the additional audio content comprisesmixing the first channel and the audio notification, and wherein mixingthe second portion of the audio content with the additional audiocontent comprises mixing the second channel and the audio notification.16. The method of claim 13, further comprising: determining thatparticular samples of the at least one fourth audio signal exceed afirst threshold level; and reducing levels of the particular samplesbelow the first threshold level.
 17. The method of claim 13, furthercomprising: sending, via a first network interface to the secondplayback device, the at least one fourth audio signal representing atleast a second portion of the audio content, wherein the first playbackdevice comprises the first network interface; and receiving, via asecond network interface, the at least one fourth audio signal, whereinthe second playback device comprises the second network interface.
 18. Atangible, non-transitory computer-readable medium comprising programinstructions that are executable by at least one processor such that amedia playback system comprising a first playback device and a secondplayback device is configured to: receive audio content; play back, viaat least one first audio transducer, at least one first audio signalrepresenting at least a first portion of the audio content, wherein thefirst playback device comprises the at least one first audio transducerand a first housing carrying the at least one first audio transducer;play back, via at least one second audio transducer, at least secondaudio signal representing at least a second portion of the audio contentin synchrony with playback of the at least one first audio signal on thefirst playback device, wherein the second playback device comprises theat least one second audio transducer and a second housing carrying theat least one second audio transducer; receive additional audio content;generate at least one third audio signal representing at least the firstportion of the audio content and the additional audio content, whereinthe instructions that are executable by the at least one processor suchthat the media playback system is configured to generate the at leastone third audio signal comprise instructions that are executable by theat least one processor such that the media playback system is configuredto mix the first portion of the audio content with the additional audiocontent; generate at least one fourth audio signal representing at leastthe second portion of the audio content and the additional audiocontent, wherein the instructions that are executable by the at leastone processor such that the media playback system is configured togenerate the at least one fourth audio signal comprise instructions thatare executable by the at least one processor such that the mediaplayback system is configured to mix the second portion of the audiocontent with the additional audio content; play back the at least onethird audio signal via the at least one first audio transducer; and playback the at least one fourth audio signal via the at least one secondaudio transducer in synchrony with playback of the at least one thirdaudio signal on the first playback device.
 19. The tangible,non-transitory computer-readable medium of claim 18, wherein the audiocontent comprises a first channel and a second channel of multi-channelaudio, wherein the additional audio content comprises a center channelof the multi-channel audio, wherein the instructions that are executableby the at least one processor such that the media playback system isconfigured to mix the first portion of the audio content with theadditional audio content comprise instructions that are executable bythe at least one processor such that the media playback system isconfigured to mix the first channel and the center channel, and whereinthe instructions that are executable by the at least one processor suchthat the media playback system is configured to mix the second portionof the audio content with the additional audio content compriseinstructions that are executable by the at least one processor such thatthe media playback system is configured to mix the second channel andthe center channel.
 20. The tangible, non-transitory computer-readablemedium of claim 18, wherein the audio content comprises a first channeland a second channel of multi-channel audio, wherein the additionalaudio content comprises an audio notification, wherein the instructionsthat are executable by the at least one processor such that the mediaplayback system is configured to mix the first portion of the audiocontent with the additional audio content comprise instructions that areexecutable by the at least one processor such that the media playbacksystem is configured to mix the first channel and the audionotification, and wherein the instructions that are executable by the atleast one processor such that the media playback system is configured tomix the second portion of the audio content with the additional audiocontent comprise instructions that are executable by the at least oneprocessor such that the media playback system is configured to mix thesecond channel and the audio notification.